The effect of cortisol on the binding of actinomycin D to and on the template activity of isolated rat liver chromatin

DNA Damage and Chromatin Conformation Changes Confer Nonhost Resistance: A Hypothesis Based on Effects of Anti-cancer Agents on Plant Defense Responses

Over the last decades, medical research has utilized DNA altering procedures in cancer treatments with the objective of killing cells or suppressing cell proliferation. Simultaneous research related to enhancing disease resistance in plants reported that alterations in DNA can enhance defense responses. These two opposite perspectives have in common their effects on the center for gene transcription, the nuclear chromatin. A review of selected research from both anticancer- and plant defense-related research provides examples of some specific DNA altering actions: DNA helical distortion, DNA intercalation, DNA base substitution, DNA single cleavage by DNases, DNA alkylation/methylation, and DNA binding/exclusion. The actions of the pertinent agents are compared, and their proposed modes of action are described in this study. Many of the DNA specific agents affecting resistance responses in plants, e.g., the model system using pea endocarp tissue, are indeed anticancer agents. The tumor cell death or growth suppression in cancer cells following high level treatments may be accompanied with chromatin distortions. Likewise, in plants, DNA-specific agents activate enhanced expression of many genes including defense genes, probably due to the chromatin alterations resulting from the agents. Here, we propose a hypothesis that DNA damage and chromatin structural changes are central mechanisms in initiating defense gene transcription during the nonhost resistance response in plants.

Replicative activity and actinomycin binding in mouse diploid fibroblasts (in vitro ageing)

Populations of embryonic mouse fibroblasts undergo 10 +/- 2 doublings in vitro prior to cessation of growth. We have studied various properties of the DNA of such cells as they undergo this process of in vitro ageing. Following a 1-h pulse with [3H]thymidine the labelling of growing cell populations decreases progressively with serial subcultivation. At early passage levels, the decrease in labelling between passages is rapid, but after about five passages the decline is much slower. Following a long pulse with [3H]thymidine (up to 4 days), up to 50% of the cells in the final passage become labelled. The binding of [3H]actinomycin to nuclei decreases progressively during serial subcultivation. Under conditions of quiescence, induced by serum deprivation, the cells withdraw from the S-phase. Feulgen cytophotometry reveals a wide spectrum of cellular DNA contents in terminal cultures, with 38% of cells possessing more DNA than equivalent early passage cells. Under these conditions, 40% of the fibroblasts bind less actinomycin than any early passage cells. Neither variations in DNA amount nor differences in cell-cycle phases can explain these alterations, which are thought to be related to age-dependent changes in chromatin condensation.

Dexamethasone-binding proteins in cytosol and nucleus of rat thymocytes. Purification of three receptor proteins

Dexamethasone-binding proteins from the cytosol and the nucleus of rat thymocytes were analyzed by ion-exchange chromatography on DEAE-cellulose. Three dexamethasone-binding proteins were revealed in cytosol, one in the flow-through (DE-1) and two (DE-2 and DE-3) eluting from the column with 0.13 M and 0.23 M NH4Cl, respectively. In nuclear extracts only one receptor fraction, present in the flow-through, could be detected. By a combination of affinity chromatography on Cl-Sepharose to which dexamethasone 21-methanesulfonate was linked through a disulufide bond and DEAE-cellulose chromatography, three receptor proteins were highly purified from cytosol, with molecular weights of 45 000, 72 000 and 90 000 and one from nuclear extracts with molecular weight of 72 000. Antibodies to the 45 000-Mr and 90 000-Mr proteins were elicited in rabbits. The antibodies to the 45 000-Mr protein cross-react with the 90 000-Mr. Similarly, the antibodies to the 90 000-Mr protein cross-react with the 45 000-Mr protein. Antibodies to either of the two proteins immunoprecipitate 60--70% of the dexamethasone-binding activity of rat thymus cytosol. Immunoaffinity chromatography of cytosol and nucleosol on columns of Sepharose linked to the IgG against either the 45 000-Mr or the 90 000-Mr protein leads to binding of these proteins on the columns but not of the 72 000-Mr species. Two nuclear polypeptides with molecular weights of 36 000 and 38 000 remain attached to the immunoaffinity column; these polypeptides may represent degradation products of the cytoplasmic receptor upon entrance into the nucleus. Antibodies against two dexamethasone-binding proteins from rat liver cytosol immunoprecipitate the 45 000-Mr cytosol receptors from rat thymus.

Dexamethasone binding to chromatin, inhibition of in vitro RNA synthesis, and therapeutic effect on human lymphosarcoma

A very high degree of specific dexamethasone binding to chromatin and a marked in vitro inhibition of RNA-synthesizing capacity of purified lymphoma cell nuclei was found to correlate closely with the very strong cytolethal effect of glucocorticoids on lymphoma cells (in this case neither B- nor T-cells) of a young patient, whose condition rapidly and unexpectedly deteriorated after a total dose fo 90 mg of Prednisone given during a two day period; and in spite of prophylactic antihyperuricaemia treatment, the patient subsequently died. In this case the amount of glucocorticoid bound specifically by lymphoma chromatin was about 400% larger than is normally found in chromatin isolated from normal human thymus cells in persons on this age. The in vitro inhibition of RNA-Synthesizing activity measured with the aggregate enzyme and with isolated nuclei from lymphoma cell-nuclei by dexamethasone correlates closely to the specific dexamethasone binding capacity of chromatin. Thus a better prediction of the therapeutic effect of such lymphosarcoma cells to glucocorticoid may be possible.

Nuclear binding of tritiated actinomycin in surface epithelial cells from normal stomach and atrophic gastritis

Triated actinomycin binding to DNA is closely linked to the degree of repression in chromatin. 3H-AM binding to DNA is the most pronounced in nuclei of cells committed into cycle. Inversely, in cells in the last steps of their differentiation or (and) in the resting state (non-dividing cells), 3H-AM binding for DNA is diminished down to a baseline since it is limited by the deoxynucleoproteins. Epithelial cells of stomach mucosa and duodenum demonstrate an increased cell uptake of tritiated actinomycin from the surface to the bottom of the pits. In severe gastritis and in intestinalysed metaplasia this was abolished: with a uniform enhancement of 3H-AM binding. These findings seem to indicate that these cells are derepressed.

Binding of the partially purified glucocorticoid receptor of rat liver to chromatin and DNA

The binding of the glucocorticoid receptor of rat liver to chromatin and DNA has been studied with crude and partially purified preparations of cytosol receptor labelled with [3H]-triamcinolone acetonide in vitro. The use of crude preparations of receptor and increasing protein concentrations leads to an apparent saturation of chromatin and DNA, suggesting a limited number of high affinity nuclear acceptor sites for the receptor. Appropriate controls indicate that the observed saturability of chromatin acceptor sites is due to the presence in crude receptor preparations of heat-stable protein factors which interfere with the binding of the receptor to the genome; whereas the apparent saturation of DNA is due to contamination with deoxyribonucleases. If the activated complex of receptor and triamcinolone acetonide (R-TA) is partially purified to a step where it is free from nucleases and inhibitors, its binding to both chromatin and DNA is linearly dependent on the concentration of free (R-TA) in the incubation medium. There is no absolute specificity with respect to the source of DNA or chromatin, although liver chromatin has considerably higher receptor binding capacity than chromatin from avian erythrocytes. The rate kinetics of association and dissociation for the binding of (R-TA) to DNA and chromatin are very similar, but DNA exhibits a 10-fold higher receptor binding capacity than chromatin. These data, in conjunction with the effect of poly-(D)-lysine and and NaCl on the binding of (R-TA) to chromatin and DNA, suggest that most of the receptor molecules bound to chromatin in vitro interact with the "accessible" DNA stretches. Although a small population of receptor molecules may bind specifically to target tissue genome, the detection of these specific sites against the background of unspecific binding is not possible with unfractionated chromatin or DNA preparations.

Movement of histones in chromatin induced by shearing

Methylation of accessible DNA within chromatin by restriction modification methylases from Haemophilus influenzae was used to detect movement of histones along the DNA strand during chromatin manipulation. Methylation at different stages of chromatin preparation was followed by titration of the nucleoprotein with ploy(D-lysine), digestion of chromosomal proteins with pronase and analysis of the DNA-poly(D-lysine) complex in steep cesium chloride gradients. Comparison of the specific radioactivities in the peak fractions of the free DNA and the DNA-poly(D-lysine) complex, respectively, reveals that lateral movement of histones, relative to specific sites in the DNA marked by restriction methylases, occurs during manipulation and fragmentation of chromatin.

Cesium chloride gradients of chromatin after treatment with micrococcal nuclease

Cesium chloride equilibrium density centrifugation shows that treatment of rat liver nuclei with low concentrations of micrococcal nuclease for extremely short periods of time results in the appearance of chromatin fractions of low protein/DNA ratio and even free DNA. The DNA of these chromatin fractions is shorter than the DNA moiety of one chromatin subunit. The amount of high buoyant density material is decreased with increasing digestion time. We conclude that this material belongs to the minor chromatin fraction which is not organized according to the subunit model.

Enhancement of soybean RNA polymerase I by auxin

When etiolated soybean seedlings are treated with the synthetic auxin, 2,4-dichlorophenoxy-acetic acid, cells of the mature hypocotyl become swollen and proliferate abnormally. This abnormal growth induced by auxin coincides with a 5- to 8-fold increase in the alpha-amanitin-insensitive RNA polymerase associated with isolated chromatin or nuclei. The alpha-amanitin-sensitive RNA polymerase activity of the auxin-treated hypocotyl was similar to that of control tissue. The increase in RNA polymerase I activity of chromatin and nuclei was maintained after solubilization and fractionation on DEAE-cellulose. Auxin thus appears to enhance RNA synthetic activity (i.e., ribosomal RNA) in mature soybean tissue by altering RNA polymerase I directly rather than by altering RNA polymerase I directly rather than by altering the chromatin template.

Pineal protein kinase: effect of enzymic phosphorylation on actinomycin D binding by, and template activity of, chromatin

The ability of protein kinase from bovinepineal gland to phosphorylate calf-thymus chromatin and thereby to alter the association between chromatin DNA and histones was investigated. Phosphorylation of calf-thymus chromatin by pineal protein kinase results in an apparent decreased binding between the histones and DNA in chromatin, as indicated by (i) an increase in actinomycin D-binding sites after phosphorylation and (ii) an increase in the template capacity of the calf-thymus chromatin after phosphorylation. F(1) histone and F(3) histone are the major histone classes in the chromatin that are phosphorylated by the protein kinase. These results support the hypothesis that pineal protein kinase may function at the transcriptional level.

Induction of malate dehydrogenase isoenzymes in livers of young and old rats

The activity of cytoplasmic malate dehydrogenase (EC 1.1.1.27) of livers of young (9-10 weeks) and old (60-70 weeks) rats decreases after adrenalectomy and increases after administration of cortisone to adrenalectomized rats. These changes are significantly lower in old rats. The induction by cortisone is inhibited by actinomycin D. Adrenalectomy decreases and cortisone increases the activity of mitochondrial malate dehydrogenase of young rats, but not of old rats. Cortisone, however, induces both mitochondrial and cytoplasmic malate dehydrogenase of the regenerating liver at both the ages. Thus, impairment of the inducibility of mitochondrial malate dehydrogenase that occurs in old age is repaired in dividing cells. Immunological studies on purified malate dehydrogenase from young and old rats show that the molecular species of the enzyme is apparently the same at both ages. The changes in activities of the enzymes seen in old age may be due to changes in template activity of the corresponding genes, which apparently do not change with age.

Detection of DNA by tritiated actinomycin D on ultrathin frozen sections

Ultrathin frozen sections of fresh liver tissue were floated on actinomycin D-(3)H. Quantitative high resolution radioautography was performed to determine the value of the method for detection of DNA by electron microscopy. A complete series of control experiments involving various treatments of frozen sections with enzymes (pronase, DNase) and 0.1 N HCl were also carried out to determine the specificity of the labeling. The results indicate the value of the method for detection of DNA directly on ultrathin frozen sections. Short treatments with pronase followed by DNase reduce the labeling to zero, whereas removal of chromosomal proteins with HCl increases the amount of radioactivity in the nucleus considerably. The results are discussed in view of the future applications opened by ultracryotomy, since radioautographic detection of various macromolecules and cellular components by labeled compound with specific affinities will now be possible.

Effect of cortisol on the thiol content of rat liver nuclear proteins

Administration of cortisol to normal or adrenalectomized rats leads within 15-30min to an increased thiol content of nuclear proteins, measured by the incorporation of iodo[(3)H]-acetate or N-[(14)C]ethylmaleimide or by colorimetric methods. The same effect is observed after incubation of isolated rat liver nuclei with corticosteroids. The increased thiol content of the nuclear proteins shows the same time-dependence as the stimulation of RNA synthesis by corticosteroids observed in vivo and in vitro. Amino acid analysis of the carboxymethylated proteins reveals that in the experiments in vivo most of the label is present as carboxymethylcysteine with small amounts of carboxymethyl-lysine and carboxymethylhistidine, whereas in the experiments in vitro more carboxymethyl-lysine and carboxymethylhistidine than carboxymethylcysteine are found. The increase in the content of thiol groups is due to cleavage of the disulphide bridges between the nuclear proteins. Polyacrylamide-gel electrophoresis of the acid-soluble fraction reveals that most of the iodo[(3)H]acetate label is incorporated into a non-histone fraction with a molecular weight of approx. 45000 whereas in the acid-insoluble fractions many protein bands are labelled.